Hydrolysis of anion

Fig. 30. Pig liver esterase-catalyzed hydrolysis of anionic DMS-ester complexes...

Anionic micellar systems were found to increase the rate of the acid catalyzed hydrolysis of acetylsalicylic acid (Nogami et al., 1962), methantheline bromide (Nogami and Awazu, 1962), n-butyl acetate, t-butyl acetate, ethyl p-aminobenzoate, and ethyl o-aminobenzoate (Sakurada et al., 1967), but decreased that of methyl benzoate slightly (Sakurada et al., 1967). The acid catalyzed hydrolysis of anionic amphi-philes also generally tend to be accelerated by micellization (Table 5). The rates of the acid catalyzed hydrolyses of sodium sulfoethyl do-decanoate, sodium undecanoate, and sodium sulfobutyl caprylate are significantly greater in micellar than in non-micellar solutions while that of sodium dodecyl sulfoacetate is unaffected by micelle formation (Meguro and Hikota, 1968). 

Other interesting examples of reactions between polyions carrying catalytically active substituents and simple substrates are the hydrolysis of anionic esters in the presence of poly-(4(5)-vinyl imidazole) (27) and the oxidation of ascorbic add or hydroquinone by atmospheric oxygen which is powerfully catalyzed in solutions containing the Cu(II) complex... 

In Section 18-8 we discussed the hydrolysis of anions of weak acids. For example, we found that for CH3COO and CN ions,... 

Oxidation State Acid Name of Acid Thermal Stability and Acid Strength Oxidizing Power of Acid Sodium Salt Name of Salt Thermal Stability Oxidizing Power and Hydrolysis of Anion Nature of Halogen... 

There is a similar difference in mechanism between closely related groups of compounds in hydrolysis of phosphate esters. Monoester hydrolysis proceeds by an initial dissociative step, but hydrolysis of anions of diesters takes place by bimolecular nucleophilic attack of solvent at phosphorus. Further studies of mechanisms of reaction of phosphate esters have been described. ... 

The rate of hydrolysis of anionic and particularly non-ionic esters catalysed by long chain hydroxamic acids is increased by the presence of micelles of hraadecyl-trimethylammonium bromide. ... 

Hydrolysis of anions and cations produces non-neutral solutions. 

Inspired by the many hydrolytically-active metallo enzymes encountered in nature, extensive studies have been performed on so-called metallo micelles. These investigations usually focus on mixed micelles of a common surfactant together with a special chelating surfactant that exhibits a high affinity for transition-metal ions. These aggregates can have remarkable catalytic effects on the hydrolysis of activated carboxylic acid esters, phosphate esters and amides. In these reactions the exact role of the metal ion is not clear and may vary from one system to another. However, there are strong indications that the major function of the metal ion is the coordination of hydroxide anion in the Stem region of the micelle where it is in the proximity of the micelle-bound substrate. The first report of catalysis of a hydrolysis reaction by me tall omi cell es stems from 1978. In the years that... 

In base the tetrahedral intermediate is formed m a manner analogous to that pro posed for ester saponification Steps 1 and 2 m Figure 20 8 show the formation of the tetrahedral intermediate m the basic hydrolysis of amides In step 3 the basic ammo group of the tetrahedral intermediate abstracts a proton from water and m step 4 the derived ammonium ion dissociates Conversion of the carboxylic acid to its corresponding carboxylate anion m step 5 completes the process and renders the overall reaction irreversible... 

Deamidation of soy and other seed meal proteins by hydrolysis of the amide bond, and minimization of the hydrolysis of peptide bonds, improves functional properties of these products. For example, treatment of soy protein with dilute (0.05 A/) HCl, with or without a cation-exchange resin (Dowex 50) as a catalyst (133), with anions such as bicarbonate, phosphate, or chloride at pH 8.0 (134), or with peptide glutaminase at pH 7.0 (135), improved solubiHty, whipabiHty, water binding, and emulsifying properties. 

The most common oxidation state of niobium is +5, although many anhydrous compounds have been made with lower oxidation states, notably +4 and +3, and Nb can be reduced in aqueous solution to Nb by zinc. The aqueous chemistry primarily involves halo- and organic acid anionic complexes. Virtually no cationic chemistry exists because of the irreversible hydrolysis of the cation in dilute solutions. Metal—metal bonding is common. Extensive polymeric anions form. Niobium resembles tantalum and titanium in its chemistry, and separation from these elements is difficult. In the soHd state, niobium has the same atomic radius as tantalum and essentially the same ionic radius as well, ie, Nb Ta = 68 pm. This is the same size as Ti ... 

Excessive hydrolysis of polyacrylamide in situ can promote undesirable polymer precipitation in the reservoir. The rate of this hydrolysis decreases with increasing level of anionic comonomers such as AMPS (130). 

Hydrolysis of aluminum alkoxides is also used commercially to produce precursor gels. This approach avoids the introduction of undesirable anions or cations so that the need for extensive washing is reduced. Although gels having surface area over 800 m /g can be produced by this approach, the commercial products are mosdy pseudoboehmite powders in the 200 —300 m /g range (28). The forming processes already described are used to convert these powders into activated alumina shapes. 

Cristobahte can also form on vitreous siUca at temperatures as low as 400°C when the pressure is equal to 35 MPa (<350 atm) and the glass is immersed in weak NaOH solutions (108). In stronger NaOH solutions, quart2 is formed. The formation of the crystalline phases is a result of the hydrolysis of the anions present. No crystallisation occurs with HF, H2SO4, and H PO in KHSO solutions or in pure water. 

Hydroxides. The hydrolysis of uranium has been recendy reviewed (154,165,166), yet as noted in these compilations, studies are ongoing to continue identifying all of the numerous solution species and soHd phases. The very hard uranium(IV) ion hydrolyzes even in fairly strong acid (- 0.1 Af) and the hydrolysis is compHcated by the precipitation of insoluble hydroxides or oxides. There is reasonably good experimental evidence for the formation of the initial hydrolysis product, U(OH) " however, there is no direct evidence for other hydrolysis products such as U(OH) " 2> U(OH)" 2> U(OH)4 (or UO2 2H20). There are substantial amounts of data, particulady from solubiUty experiments, which are consistent with the neutral species U(OH)4 (154,167). It is unknown whether this species is monomeric or polymeric. A new study under reducing conditions in NaCl solution confirms its importance and reports that it is monomeric (168). 8olubihty studies indicate that the anionic species U(OH) , if it exists, is only of minor importance (169). There is limited evidence for polymeric species such as Ug(OH) " 25 (1 4). 

N HCl) are necessary for the hydrolysis of The [B22H22] anion is the most hydrolytically stable borane anion, withstanding even 3 NUCl... 

The most important discovery in dyeing cellulose with reactive dyes was the appHcation of Schotten-Baumaun principles. Reaction of alcohols proceeds more readily and completely in the presence of dilute alkali, and the cellulose anion (cell- O ) is considerably more nucleophilic than is the hydroxide ion. Thus the fixation reaction (eq. 1) competes favorably with hydrolysis of the dye (eq. 2). 

The transition state for the rapid hydrolysis of the monoanion has been depicted as involving an intramolecular general acid catalysis by the carboxylic acid group, with participation by the anionic carboxylate group, which becomes bound at the developing electrophilic center... 

A catalyst is defined as a substance that influences the rate or the direction of a chemical reaction without being consumed. Homogeneous catalytic processes are where the catalyst is dissolved in a liquid reaction medium. The varieties of chemical species that may act as homogeneous catalysts include anions, cations, neutral species, enzymes, and association complexes. In acid-base catalysis, one step in the reaction mechanism consists of a proton transfer between the catalyst and the substrate. The protonated reactant species or intermediate further reacts with either another species in the solution or by a decomposition process. Table 1-1 shows typical reactions of an acid-base catalysis. An example of an acid-base catalysis in solution is hydrolysis of esters by acids. 

Schaub ° introduced methyl groups at both the 16a- and 17a-positions by 1,4-addition of methylmagnesium iodide to the A -20-ketone (8) followed by methylation of the intermediate 16a-methyl-17-enolate anion (9) with methyl iodide. After hydrolysis of the tetrahydropyranyl ether group a 40% yield of the 16,17-dimethyl derivative (10) was obtained. With the corresponding 3j -acetoxy derivative, the yield of (10) is only 20%. 

Hydrolysis of the trifluoromethyl group of 2 tnfluoiomethylimidazoles is promoted by the formation of the anion, which readily eliminates fluoride. The resultant ditluorodiazafulvene then easily adds water The remaining steps in the hydrolysis ate predictable When aqueous ammonia is used, 2-cyanoimidazoles result [40] (equation 4])... 

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